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San Francisco 5, Us 2, Lehr 1, John 1, Brown 1, Hud 1, Cisco 1, Lotus 1, Philip 1, Psi 1, Germany 1, Horizontal 1, Grout 1, San Francisco Or California 1, Kobe 1, California 1, Unbonded 1, Los Angeles 1,
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  SFGTV2    [untitled]  

    March 11, 2013
    8:00 - 8:30am PDT  

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>> welcome to the department of building inspections brown bag lunch series. we are very pleased to have a look at the stuff we're always talking about which is how things get built. we are here in the middle of a construction site in san francisco, mercy housing, being
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built between night and 10th, between market and mission streets. we have all of the people who are part of the project, including the contractors, the design engineers, soil engineers, structural folks. i think we should start by asking the question, what is a high-rise building? what -- what makes this different from any other building? we have the architect for this project. this is actually two projects? >> that is correct. we are building a little over 100 units, hud found it, affordable housing. there is a community center, child development center, a youth center, and there are a couple of retail spaces, the tenant of which is still to be determined. >> are these high-rise buildings? >> they are. >> a high-rise building is a building that is more than 75 feet from the point of fire department access on the ground
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to the floor of the highest occupied floor of the building. >> correct. >> i'm glad we agree. it is important to agree. this is a high-rise building. this will also be a high-rise building. they started construction yesterday. are the standards for a high- rise building for affordable housing, sponsored by the government, are the standards of construction the same as they would be if we were to build a high-rise luxury building? >> yes. >> there is no institutionalized double standard in the building code. we have the same standard of safety, regardless of income? >> that is true. >> you design these buildings, but who is hiring you? >> mercy housing, the developer. >> what is your role in construction? >> personally? >> your firm. >> we designed the building, we work with the team of engineers to design the systems. we permited the building and we
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will come out and observe the construction to make sure that the construction conforms to the intent of the permit it documents. >> one of the things you mentioned, and what if you tell us though name of your firm. one of the things that was mentioned is they coordinate with the other engineering and design people and the construction firm, and one of the major problems with these kinds of construction projects is coordination, making sure that everybody is building the same building and everything fits together right. in large measure, that is the architect's job. do you make sure that the structural stuff fits together, with the architecture and the mechanical? >> that is where we earn most of our money. >> that is difficult? >> no question, we had cahill come on board at the later stages of design to help with
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the construction, details, flexing of systems, that sort of thing. >> we're fortunate today to have john with us, who was a soil engineer. one of the design teams, one of the original first persons to be looking at this project is the soil engineer. they look at where the building will be built, what is the soil like, and how we make the building hit the ground. people say, you go down to bedrock. are we going down to bedrock? is there bad rap here? >> -- is there bad rap here? >> darrius bad rap, but it is deep. below the march lehr, 35 feet down is where we start. it is dense, hard sand, almost as hard as concrete. these piles go down about 15 feet into that sand.
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of the lotus transferred from the pile caps -- the load is transferred from the pile caps into the dense san lehr. >> there is a pile cat. what that means is after they put in the pile, they put in a steel cap? >> it is a concrete cap. it ties more than one piled together. >> that transfers the load from the building structure onto the pile. >> that is correct. >> what is the potential for earthquake movement on this kind of soil? >> this area, the ground water is deep, so you do not have to worry about the liquefaction. you have to worry about the loose sand during an earthquake. we estimate between 2 inches and 3 inches of settlement. these piles will hold the building up and the ground will settle around the piles and not cause damage to the structure. they will screw this into the ground by using a combination of
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forces. it will push and twisted into the ground. the upper 20, 30 feet goes easily, and then it starts to tighten. then at some point, it could actually stop the pile. the resistance could be so strong that it will sure off the pile and that is when we stop. >> your firm or somebody here is a special inspector, paying attention to how this is done? >> that is correct. we are observing what is done. >> we get reports saying, yes, it a mess -- and met the requirements for here were the problems in this is how they fixed it. what are they doing? >> they are screwing it into the ground. these are the marks. for every foot, the steel guy is recording the pressure on the steel. about how many of these will we have for the building? >> this building has about 200
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of these. >> this is steve from substructures support, doing this substructure work. do these all but filled with concrete? >> yes, they do. once they are installed, we will come back and fill them. sometimes we will put concrete in them so the concrete crew can put in their forms and rebar. they work in close proximity to this particular operation. >> can you tell us anything about this gigantic rig? >> it is made in germany. it is a very high-powered drilling rig, basically. the rig itself is off the shelf , adapted for our particular installation and the methodology we have adapted and used here is the right combination of pork, crowd, and advancement
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rate -- of torque, crowd, and advancement right. >> this is a quiet compared with other installations. >> that is the distinct advantage. when you were pounding in downtown san and cisco, there are a lot of noise complaints with businesses and restaurants. this is a lot quieter and perhaps maybe a little more costly and slower than a typical pile driving rig, but the advantages are that it is quiet and you are not disturbing neighbors and it makes the city officials jobs easier and keeps the residence and neighbors happier. >> we get a lot of complaints when people are pile driving, and one of the things the department of building inspection does is issue special permits for pile driving noise and we try to figure out who will be the least impact it or what will have the most were the least impact on businesses and restaurants. we're finding fewer places where
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we can insert that pile driving and have acceptable impact. i think we're seeing more and more of this kind of thrilled piles. >> i was most intrigued by your definition of a high-rise. you said and the building over 75 feet. >> to the floor of the highest floor of occupancy, not the top of the building. >> on the peninsula, anything over four stories is essentially considered a high-rise. if 70 or 75 feet is a high-rise, how would you describe buildings that are three stories, five stories? do they have names and terms of the classification of the building? >> they do. since 1994 we used the california building code. prior to that we used the san francisco building code.
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if everybody uses the same building code and everybody defines it the same way, what is a building less than a high- rise? not a high-rise. people in formally call that a mid rise building. there is no official definition. this is just not a high-rise building. they use the same code on the peninsula and the central valley and everywhere and at los angeles. >> from the time when the permit is issued and the plans are drawn. >> how long will it take to build these? >> two years apiece. >> that is fairly basic. >> about 22 months for the smaller one and 24 months for the bigger one. >> any idea how long it took to get the permits? >> i have been working on this project since 2002. we submitted to planning in 2004 probably. we actually reconfigured the
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building once. it took us about three years to get the title and design and about one year to get the building permit. >> that sounds like a traditional san francisco building, and that is fairly quick. we think about the process you have to go through to approve the use of the space. is not just the technical issue, but just the use approval is complicated. in this case we probably did not have many appeals. in many cases we have neighborhood involvement where there are appeals and changes. only reconfiguring wants is doing a good job. >> the building was just begun yesterday, to the building over here of which is based on the same construction technique i presume. we have drilled pilings, the building cap, and how many is this? >> 12 stories. right now we are on the ninth floor. >> how long does it take from
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floor to floor to get ready to pour? >> about 2 1/2 weeks from floor to floor. >> de uva use any of the material and the forms? >> the material is recycled. >> one of the ways that buildings are designed typically is they are stacked so it is repetitive, so the shafts go up and the structures are one on top of the other. that makes you able to build it the way you are doing it. one of the things that i see is house and after they were on the floor that they already have the work inside the building going. they have the plumbing, the drain, waste, that lines, of fire sprinklers, interior partitions. >> typically we are three floors below. we start the framing. each floor is different progression. the first floor takes the longest.
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>> the major issues that follow include plumbing, fire sprinklers. >> mechanical. >> what is mechanical? >> heating and air-conditioning. >> these are residential units? >> correct. >> there are more services that may be an empty commercial office? >> this is true. >> let's work our way out. we have drilled, poured the first floor slab. >> you get the first floor slab port, then we start on the vertical columns and walls. then we start the decking. we are always chasing the cycle. >> how thick is the ground floor slab. >> 10 inches. the other floors are about 7.5. >> you are a structural engineer. you are one of the engineering firms that the city hired after the 1989 earthquake to evaluate
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the damage residents. we have a long and good working relationship. they are building this and they are doing post-tension slabs. what is that? >> it is a construction method that uses high strength tendons to work with concrete and make the concrete sections a better section for bending. it has a lot of benefits. the reduces the thickness of the slab, it reduces the number of cracks. the result is a nice, flat slab with very little cracks. >> we now have a piece of this post-tension material. tell us what this is and why this is so wonderful, which is. >> this is called unbonded, because of this plastic sheeting. it is not bond to the concrete.
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>> why do you want to do that? >> because there are two methods of decreasing stress. one is posttensioning. the other is pretensioning. this method that we are using is a very conventional for on-site stressing of the slab. what it does is it does not bond to the concrete. you put the form up, he placed the attendance. >> this will be or is not all. inside the floor. -- this will be horizontal, inside the floor. >> this is the anchored and of it. there is a parable -- parabolic profile tendons. their lowest in the mid span and they are the highest above.
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what happens is once that you place these inside of the form work and you have the other reinforcements, you pour the concrete. at a certain point where you have adequate curing of the concrete, which is usually about two-thirds of the strength of the concrete, then you jack these and pull them. >> you pull them with hydraulics. you attention it. >> it does two things. it puts large. compression into the concrete slab. because of the profile, it also lifts the slab. that is how you counteract some of the debt load -- dead load. >> how long is this intended to last? >> the life of the structure, basically 50 years. but it could go on. >> let's talk about that.
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the anticipated life of the building is? >> usually 50 years. >> this is a big issue in san francisco. i say that because we're now seeing buildings considered historic resources, if they are over 50 years old, they may have historic value of any sort. seems once a building has reached a certain age, 50 years or more, it could be here a long time. we do not really go through buildings every 20 years. we see some assemblies put into buildings, especially high-rise buildings, window wall assemblies, which have a reasonable life span, maybe 30 years. what that means is after 30 years, you have to expect to go in and replace the window wall assembly and all of its pieces. in some cases, the financing and
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the owners, wherever it is, are not really aware of all of these different life expectancies with the building. it is an issue that we're trying to sort out. we say this is what we anticipate a reasonable life span of the building to be. the components need to be suitable for that anticipated life span. this is something that has to be because a guy easily take them out and replace them. >> that is right. >> this is one of the determining factors of the life expectancy. does that make sense? >> that is right. usually, there are no problems with post pension slabs. corrosion could be an issue if anchors are not put incorrectly. >> you see these anchors? >> if you look at the edge of the slab, you will cd circular holes that are filled with
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grout, and the cable is cut. >> as you look at the crane, you see on the edge of the slab holes, and there are typically three together. >> it depends. >> it depends on where they are. there will put a hydraulic jack on that, tension in it, and philip. we need to make sure that water is not get in there or you may have corrosion. i think we need to back up a little bit. this building is essentially a concrete building. it has steel reinforcing in it because concrete is very strong with compression, when it is pushing down, but it is not very strong in other dimensions. you could imagine taking a long concrete bar and bending it, it will break easily. not much capacity with attention. -- not much capacity with
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tension. used to steal for the tension forces. this building is sort of a traditional, prescriptive we designed concrete building. that means they are building to building strictly in accordance with the cookbook requirements of the san francisco or california building codes. it this is a building we are very confident will perform the way we expect it to perform because we have built tens of thousands of buildings just like these, the structural systems. >> that is correct, it is fairly conventional in terms of residential construction. >> will we have our concrete walls, reinforced with steel. i have a couple of pieces of steel. >> this is called mild steel. this is not high strength steel, which is used for the attendance. -- better used for the tendons.
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these are used for columns and foundation. these are 60 psi. >> this is available in all different sizes, eighths of an inch? >> number 3 is 3/8. >> number 4, number five, maybe 5/8. let's pass this around. it is heavy. it is deformed. tell us what that means. >> in the surface of the rebar, that is what engages the reader are with the concrete and creates the section that works with the compression. >> it is rough, and roughness of it connects or secures to the concrete. when i was in kobe, japan, right after the 1995 earthquake,
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looking at some of the damage, i saw some failure of concrete structures where they had non- deformed read bar -- rebar, smooth steel, and concrete just pulled right off. this has been deformed, which has been used 50, 100 years? >> i believe after the 1930's, he formed rebar is what is used. >> this is standard. that is used in the vertical wall, almost any place except for the special slabs. >> the slab also has reinforcement, but it has much less than a conventional slab. >> they poured the slab one grade, sitting right on the ground? >> it is one great, but it is designed as a structural slab. we are counting on the bearing of the slab on grade because of
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the poor soil underneath. we used a structural slab. is interconnected, going back to what john mentioned with the pilings and the caps. >> even if the ground underneath the building settles, which it could do it in an earthquake, the slab will retain its application and integrity and strength. >> that is why it is 10 inches, thicker than your normal 5 inch slab. >> why should it be thicker than the floor above? >> because the slabs on grade is a conventional slap, it is not post tension. >> one of the things the building designers do is to make the floor as thin as they reasonably can. >> there are several benefits to that. first of all, it reduces the mass of the building.
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we have 7.5 inch slab. conventional slab would probably be 10.5 inches, which is about 25% more concrete mass. it also reduces the overall floor to floor height, which helps with the architectural facade and the square footage. >> one of the things people are always looking at is decreasing the floor to floor height, especially in san francisco where we have clearly defined height limits, and maybe could squeeze another story and there if you are good at it. we see a lot of people struggling with the thickness of all these assemblies, both the structural assembly and non structural which might be above the ceiling, where we have the heating, ventilation, plumbing, fire sprinklers. you say that the finish of the concrete slab can be exposed?
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>> in our building that is the case. >> that would mean you have exposed footings? >> the utilities, they are stealing the utilities, is that right? -- they are ceiling utilities, is that right? >> i am with the associated architects. within the dwelling units, which are not air-conditioned, the concrete ceiling is typically exposed. in most public areas, which may be heated and cooled with forced air, that is where you get the dropped ceiling. also, corridors and public areas. >> the dwelling units do not have air-conditioning? >> they do not. they have heating but not air conditioning. >> do they have outside air? >> absolutely, they have windows and they also have a system called z-duct, which provides
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for a share even when the windows are closed. >> one of the reasons they have the systems, ever since 1974, chapter 12-day of the building code requires that you have sound transmission isolation between dwelling units so they cannot hear their neighbors, and between the residential units and the cars at outside. that specifically says that if you are in one of these noise areas, which are on the transit corridor, that you must design the building such that you can ventilate the resident units with the windows closed, meeting all the noise control requirements. you close the windows and you still have enough ventilation, which is why people use z-ducts. >> that is correct. the bathroom and kitchen exhaust fans are on at a low-level all the time.
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even when the windows are closed they are always pulling in adequate amounts of ventilation from the exterior. >> are there any other special noise control features? >> the code required what is called sound transmission walls between the units. between units above and below also. the concrete floors are very good at deadening air-form sounds, but impact sounds are harder to control. you could imagine a shoe reverberating through there, so we have to provide padding through hard finish material such as title or sheet vinyl to death in the sound. -- to daeden that sound. >> that means there is a specific floor assembly that goes down. maybe a carpet with pad. people 5, 10 years from now say
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i will replace the carpet or the linoleum, they do not fully understand that as part of the sound transmission assembly, required by the code, and to protect them. in many cases we see lawsuits from the generation of sound transmission. also, the walls between dwelling units, they are making the walls out of light gauge metal studs. in order to make the sound transmission work, you have to do these exactly right. you have to have the sound isolation between the sheet rock and the stud, and stud and the sheet rock on the other side. how are you doing that? >> we have a couple different wall assemblies. there is one that goes between units, st. ford assembly with two layers of dry wall -- straight forward assembly with two layers of dry wall. then we have a sound